I dont know about un-deleting, but you could use this package to reset the default admin user: https://our.umbraco.org/projects/developer-tools/umbraco-admin-reset/

Thanks for the suggestion. I had a look at that project and it effectively just resets the password and unlocks the admin user. Doesn't do anything with the user types. Below is pretty much it:

var user = UmbracoContext.Current.Application.Services.UserService.GetUserById(0);
            if (user != null)
            {
                user.Username = "Admin";
                user.IsApproved = true;
                user.IsLockedOut = false;

                //Save changes
                UmbracoContext.Current.Application.Services.UserService.Save(user);
                //Change password
                UmbracoContext.Current.Application.Services.UserService.SavePassword(user, "Admin1234!");
            }

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